There are many different types of amino acid. One of these is phenylalanine. The diagram shows the structure of a molecule of phenylalanine. [Figure 4.0 showing the chemical structure of phenylalanine: NH2-CH2-C(COOH)-H] (a) Phenylalanine is metabolised by an enzyme with the name PAH. (i) Name the human organ that metabolises amino acids such as phenylalanine. [1] (ii) Explain how the shape of a PAH enzyme molecule is important to enable phenylalanine to be metabolised. [3] (b) A rare gene mutation reduces the activity of the PAH enzyme. The mutation results in an increased concentration of phenylalanine in the blood. This condition can cause damage to the brain. (i) Describe what is meant by the term gene mutation. [2] (ii) Explain how a person with the condition should change their diet to reduce the risk of damage to the brain. [3] (iii) The gene mutation produces a recessive allele, h. A person with a heterozygous genotype is described as a carrier. A carrier will not show symptoms of the condition. Complete the genetic diagram to show the probability of two carriers reproducing to have offspring with the condition. [Figure 4.1 showing a Punnett square for gametes and offspring] gametes probability of offspring with the condition [3]

1. (a)(i)Name the human organ that metabolises amino acids such as phenylalanine.[1]
2. (a)(ii)Explain how the shape of a PAH enzyme molecule is important to enable phenylalanine to be metabolised.[3]
3. (b)(i)Describe what is meant by the term gene mutation.[2]
4. (b)(ii)Explain how a person with the condition should change their diet to reduce the risk of damage to the brain.[3]
5. (b)(iii)The gene mutation produces a recessive allele, h. A person with a heterozygous genotype is described as a carrier. A carrier will not show symptoms of the condition. Complete the genetic diagram to show the probability of two carriers reproducing to have offspring with the condition. gametes [Figure 4.1 showing a Punnett square for gametes and offspring] probability of offspring with the condition[3]

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